By this time they had approached very near to the Tower, although the thick growth of the trees hindered them from seeing it, as it also concealed them from the eyes of any persons who might be upon the walls.  The evening light was now fast waning.  Upon the tops of the heights the sun still shone, but here in the wooded hollow, beside the sullen waters of the moat, twilight had already fallen, and soon it would be dark as night itself.  The moon rose late, and for a space there would be no light save that of the stars.

Constanza laid her finger upon her lips, and made a sign demanding caution.  Gaston understood that he was warned not to speak, and to tread cautiously, which he did, stealing along after his fairy-like companion, and striving to emulate her dainty, bird-like motions.  He could see by the glint of water that they were skirting along beside the moat, but he had never approached so near to it before, and he knew not where they were going.

Some men might have feared treachery, but such an idea never entered Gaston’s head.  Little as he knew of his companion, he knew that she was true and loyal, that she was beloved by him, and that her heart was already almost won.

Presently the girl stopped and laid her hand upon his arm.

“This is the place,” she whispered.  “Come very softly to the water’s edge, and I will show you the dark hole opposite, just above the waterline, where entrance can be made.  There be no loopholes upon this side of the Tower, and no watchman is needed where there be no foothold for man to scale the wall beneath.

“Look well across the moat.  Seest thou yon black mark, that looks no larger than my hand?  That is the entrance to a tunnel which slopes upward until it reaches a narrow doorway in the thickness of the solid wall whereby the underground chamber may be reached.  Once there, thou wilt see let into the wall a great wheel with iron spokes projecting from it.  Set that wheel in motion, and a portion of the flooring of the chamber above will descend.  When it has reached the ground, thou canst ascend by reversing the wheel, leaving always some one in the chamber below to work the wheel, which will enable thee to bring thy brother down again.  That accomplished, all that remains will be to creep again through the narrow passage to the moat and swim across once more.  Thou canst swim?”

“Ay, truly.  Raymond and I have been called fishes from our childhood.  We swam in the great mill pool almost ere we could well run alone.  Many of my stout fellows behind are veritable water rats.  If my brother be not able to save himself, there will be a dozen stout arms ready to support him across the moat.

“And what will be the hour when this attempt must be made?  What if the very moment I reached my brother his jailer should come to him, and the alarm be given through the Castle ere we could get him thence?”